The present invention is directed to using mechanical oscillators for measuring various properties of fluids (including both liquids and vapors), and more particularly to a method and system using a mechanical oscillator (resonator) for measuring physical, electrical and/or chemical properties of a fluid based on the resonator""s response in the fluid to a variable frequency input signal.
Companies are turning to combinatorial chemistry techniques for developing new compounds having novel physical and chemical properties. Combinatorial chemistry involves creating a large number of chemical compounds by reacting a known set of starting chemicals in all possible combinations and then analyzing the properties of each compound systematically to locate compounds having specific desired properties. See, for example, U.S. patent application Ser. No. 08/327,513 (published as WO 96/11878), filed Oct. 18, 1994, entitled xe2x80x9cThe Combinatorial Synthesis of Novel Materialsxe2x80x9d, the disclosure of which is incorporated by reference.
The virtually endless number of possible compounds that can be created from the Periodic Table of Elements requires a systematic approach to the synthesizing and screening processes. Thus, any system that can analyze each compound""s properties quickly and accurately is highly desirable. Further, such a system would be useful in any application requiring quick, accurate measurement of a liquid""s properties, such as in-line measurement of additive concentrations in gasoline flowing through a conduit or detection of environmentally-offending molecules, such as hydrogen sulfide, flowing through a smokestack.
It is therefore an object of the invention to measure simultaneously both the physical and the electrical properties of a fluid composition using a mechanical resonator device.
It is also an object of the invention to detect differences clearly between two or more compounds in a fluid composition by using a mechanical resonator device to measure a composition""s physical and electrical properties.
It is a further object of the invention to use a mechanical resonator device to monitor and measure a physical or chemical transformation of a fluid composition.
It is also an object of the invention to use a mechanical resonator device to detect the presence of a specific material in a fluid.
The present invention includes a method for measuring a property of a fluid composition using a tuning fork resonator, the method comprising:
placing the tuning fork resonator in the fluid composition such that at least a portion of the tuning fork resonator is submerged in the fluid composition;
applying a variable frequency input signal to a measurement circuit coupled with the tuning fork resonator to oscillate the tuning fork resonator;
varying the frequency of the variable frequency input signal over a predetermined frequency range to obtain a frequency-dependent resonator response of the tuning fork resonator; and
determining the property of the fluid composition based on the resonator response.
The method can also measure a plurality of fluid compositions, wherein the fluid compositions are liquid compositions, using a plurality of tuning fork resonators, wherein the method further comprises:
providing an array of sample wells;
placing each of said plurality of liquid compositions in a separate sample well;
placing at least one of said plurality of tuning fork resonators in at least one sample well;
applying a variable frequency input signal to a measurement circuit coupled with each tuning fork resonator in said at least one sample wells to oscillate each tuning fork resonator associated with each of said at least one sample well;
varying the frequency of the variable frequency input signal over a predetermined frequency range to obtain a frequency-dependent resonator response of each tuning fork resonator associated with said at least one sample well; and
analyzing the resonator response of each tuning fork resonator associated with said at least one sample well to measure a property of each liquid composition in said at least one sample well.
Accordingly, the present invention is directed primarily to a method using a mechanical piezoelectric quartz resonator (xe2x80x9cmechanical resonatorxe2x80x9d) for measuring physical and electrical properties, such as the viscosity density product, the dielectric constant, and the conductivity of sample liquid compositions in a combinatorial chemistry process. The detailed description below focuses primarily on thickness shear mode (xe2x80x9cTSMxe2x80x9d) resonators and tuning fork resonators, but other types of resonators can be used, such as tridents, cantilevers, torsion bars, bimorphs, or membrane resonators. Both the TSM resonator and the tuning fork resonator can be used to measure a plurality of compounds in a liquid composition, but the tuning fork resonator has desirable properties that make it more versatile than the TSM resonator.
The mechanical resonator is connected to a measuring circuit that sends a variable frequency input signal, such as a sinusoidal wave, that sweeps over a predetermined frequency range, preferably in the 25-30 kHz range for the tuning fork resonator and in a higher range for the TSM resonator. The resonator response over the frequency range is then monitored to determine selected physical and electrical properties of the liquid being tested. Although both the TSM resonator and the tuning fork resonator can be used to test physical and electrical properties, the tuning fork resonator is an improvement over the TSM resonator because of the tuning fork""s unique response characteristics and high sensitivity.
Both the TSM resonator and the tuning fork resonator can be used in combinatorial chemistry applications according to the present invention. The small size and quick response of the tuning fork resonator in particular makes it especially suitable for use in combinatorial chemistry applications, where the properties of a vast number of chemicals must be analyzed and screened in a short time period. In a preferred embodiment, a plurality of sample wells containing a plurality of liquid compositions are disposed on an array. A plurality of TSM or tuning fork resonators are dipped into the liquid compositions, preferably one resonator per composition, and then oscillated via the measuring circuit. Because the resonating characteristics of both the TSM resonator and the tuning fork resonator virtually eliminate the generation of acoustic waves, the size of the sample wells can be kept small without the concern of acoustic waves reflecting from the walls of the sample wells. In practice, the tuning forks can be oscillated at a lower frequency range than TSM resonators, making the tuning forks more applicable to real-world applications and more suitable for testing a wide variety of compositions, including high molecular weight liquids.
In another embodiment of the invention, the mechanical resonator is coated with a material to change the resonator""s characteristics. The material can be a general coating to protect the resonator from corrosion or other problems affecting the resonator""s performance, or it can be a specialized xe2x80x9cfunctionalizationxe2x80x9d coating that changes the resonator""s response if a selected substance is present in the composition being tested by the resonator.
To obtain a more complete range of characteristics for a selected fluid composition, multiple resonators having different resonator characteristics can be connected together as a single sensor for measuring the fluid composition. The resonator responses from all of the resonators in the sensor can then be correlated to obtain additional information about the composition being tested. By using resonators having different characteristics, the fluid composition can be tested over a wider frequency range than a single resonator. Alternatively, a single resonator that can be operated in multiple mechanical modes (e.g. shear mode, torsion mode, etc.) can be used instead of the multiple resonators. The resonator responses corresponding to each mode would be correlated to obtain the additional information about the composition.
The mechanical resonator system of the present invention, particularly a system using the tuning fork resonator, can also be used to monitor changes in a particular liquid by keeping the resonator in the liquid composition as it undergoes a physical and/or chemical change, such as a polymerization reaction. The invention is not limited to measuring liquids, however; the quick response of the tuning fork resonator makes it suitable for measuring the composition of fluid compositions, both liquid and vaporous, that are flowing through a conduit to monitor the composition of the fluid.